RFC 6718
Pseudowire Redundancy
RFC 6718: Pseudowire Redundancy 🎀 Okay bestie, this one is informational, so it's not a standard, just a super useful framework 💅
Written by P. Muley, M. Aissaoui, and M. Bocci, all from Alcatel-Lucent 👑. It's Category: Informational, ISSN: 2070-1721, dated August 2012 🌸. The title block doesn't list any Obsoletes or Updates entries, so this doc isn't replacing or changing any older RFC 🦋.
Abstract ✨
Okay so this doc lays out a framework 🧚 made of scenarios and the requirements that go with them, all about pseudowire (PW) redundancy 💜. You set up a group of redundant PWs between provider edge (PE) nodes in single-segment PW applications, or between terminating PE (T-PE) nodes in multi-segment PW applications. So the PE/T-PE nodes can tell each other which PW to use for forwarding PW packets, there's a new PW status for that: the preferential forwarding status of active or standby for each PW in the redundant set. It's giving organized 🫶
Status of This Memo 🌈
This document is not an Internet Standards Track specification. It's published for informational purposes 🦋
It's a product of the Internet Engineering Task Force (IETF), so it represents the consensus of the IETF community. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). Not every document the IESG approves is a candidate for any level of Internet Standard, so check Section 2 of RFC 5741 for that 💅
Info about the current status of this doc, any errata, and how to give feedback is at http://www.rfc-editor.org/info/rfc6718 ✨
Copyright Notice 💜
Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved 🔥
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication. Please review these carefully, because they describe your rights and restrictions for this document 🧐 Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they're provided without warranty as described in the Simplified BSD License 🫶
Table of Contents 🍓
1. Introduction ....................................................3
2. Terminology .....................................................4
2.1. Requirements Language ......................................6
3. Reference Models ................................................6
3.1. PE Architecture ............................................6
3.2. PW Redundancy Network Reference Scenarios ..................7
3.2.1. PW Redundancy for AC and PE Protection: One
Dual-Homed CE with Redundant SS-PWs .................7
3.2.2. PW Redundancy for AC and PE Protection: Two
Dual-Homed CEs with Redundant SS-PWs ................8
3.2.3. PW Redundancy for S-PE Protection:
Single-Homed CEs with Redundant MS-PWs .............10
3.2.4. PW Redundancy for PE-rs Protection in
H-VPLS Using SS-PWs ................................11
3.2.5. PW Redundancy for PE Protection in a VPLS
Ring Using SS-PWs ..................................13
3.2.6. PW Redundancy for VPLS n-PE Protection
Using SS-PWs .......................................14
4. Generic PW Redundancy Requirements .............................15
4.1. Protection Switching Requirements .........................15
4.2. Operational Requirements ..................................15
5. Security Considerations ........................................16
6. Contributors ...................................................16
7. Acknowledgements ...............................................17
8. References .....................................................17
8.1. Normative References ......................................17
8.2. Informative Reference .....................................181. Introduction 🦋
The whole point of PW redundancy is to keep connectivity going across the packet switched network (PSN) that the emulated service uses, even if a part of the path fails or a backup part gets switched on 💖 For example, PW redundancy makes sure the correct PW is used for forwarding emulated service packets when an attachment circuit (AC) loses connectivity because the AC failed, or when a pseudowire (PW) or PSN tunnel dies because a provider edge (PE) node failed 😭
PW redundancy uses redundant ACs, PEs, and PWs to get rid of single points of failure in the path of an emulated service 🔥 It does this while making sure only one path between a pair of customer edge (CE) nodes is active at any given time. Mechanisms that depend on more than one active path between the CEs, like 1+1 protection switching, are out of scope for this doc. That's because they may require a permanent bridge to do traffic replication, plus support for a 1+1 protection switching protocol in the CEs 🙈
Protection for a PW segment can come from the PSN layer. That could be a Resource Reservation Protocol with Traffic Engineering (RSVP-TE) label switched path (LSP) with a fast-reroute (FRR) backup, or an end-to-end backup LSP 🧚 These mechanisms can restore PSN connectivity fast enough that PW redundancy doesn't have to kick in. But PSN protection can't protect against a PE node failing or the remote AC failing. Usually that's handled by dual-homing a CE node to different PE nodes that provide a pseudowire emulated service across the PSN. So a set of PW mechanisms is required that lets a primary PW and one or more backup PWs terminate on different PE nodes 👑 An important requirement here is that changes on the dual-homed side, caused by an AC or PE failing, don't get propagated to the ACs on the other side of the network. And failures in the PSN don't get propagated to the attached CEs either 💅
Now, when PSN protection can't recover from a PSN failure, or when a switching PE (S-PE) might fail, you need mechanisms that support a primary PW and one or more backup PWs running through a different set of S-PEs or diverse PSN tunnels. For multi-segment PWs (MS-PWs), the paths are diverse because they get switched at different S-PE nodes 🌸
Either way, PW redundancy matters a lot for keeping the emulated service resilient 💜 It supplements PSN protection techniques, and it can work alongside those techniques or instead of them when they aren't available 🫶
This doc describes a framework for these applications and their operational requirements. The framework uses a new PW status called the 'Preferential Forwarding Status' of the PW 🎀 It's separate from the operational states defined in RFC 5601 [RFC5601]. The mechanisms for PW redundancy are modeled on general protection switching principles ✨
2. Terminology 💅
- Up PW: A PW that has been configured (label mapping exchanged between PEs) and isn't in any of the PW or AC defect states represented by the status codes specified in [RFC4446]. Such a PW is available for forwarding traffic 🦋
- Down PW: A PW that either hasn't been fully configured, or has been configured and is in any one of the PW or AC defect states specified in [RFC4446]. Such a PW isn't available for forwarding traffic 💀
- Active PW: An up PW used for forwarding Operations, Administration, and Maintenance (OAM) as well as user-plane and control-plane traffic 🔥
- Standby PW: An up PW that isn't used for forwarding user traffic, but it may forward OAM and specific control-plane traffic 🌈
- PW Endpoint: A PE where a PW terminates at a point where native service processing is performed, e.g., a single-segment PW (SS-PW) PE, a multi-segment pseudowire (MS-PW) terminating PE (T-PE), or a hierarchical Virtual Private LAN Service (VPLS) MTU-s or PE-rs 👑
- Primary PW: The PW that a PW endpoint activates (i.e., uses for forwarding) in preference to any other PW when more than one PW qualifies for the active state. When the primary PW comes back up after a failure and qualifies for the active state, the PW endpoint always reverts to it. Being primary is set by local configuration for the PW at the PE, and it's only required when revertive behavior is used. It doesn't apply when non-revertive protection switching is used 🧚
- Secondary PW: When it qualifies for the active state, a secondary PW is only selected if no primary PW is configured, or if the configured primary PW doesn't qualify for the active state (e.g., it's down). By default, a PW in a redundancy PW set is considered secondary. There's no revertive mechanism among secondary PWs 🙈
- Revertive protection switching: Traffic will be carried by the primary PW if all of the following is true: it's up, a wait-to-restore timer expires, and the primary PW is made the active PW 🍓
- Non-revertive protection switching: Traffic will be carried by the last PW selected as a result of a previous active PW entering the operationally down state 💜
- Manual selection of a PW: The ability to manually select the primary/secondary PWs 🎀
- MTU-s: A hierarchical virtual private LAN service multi-tenant unit switch, as defined in RFC 4762 [RFC4762] 🌸
- PE-rs: A hierarchical virtual private LAN service switch, as defined in RFC 4762 🦋
- n-PE: A network-facing provider edge node, as defined in RFC 4026 [RFC4026] ✨
- 1:1 protection: One specific subset of a path for an emulated service, consisting of a standby PW and/or AC, protects another specific subset of a path for the emulated service. User traffic is transmitted over only one specific subset of the path at a time 🫶
- N:1 protection: N specific subsets of paths for an emulated service, consisting of standby PWs and/or ACs, protect another specific subset of the path for the emulated service. User traffic is transmitted over only one specific subset of the path at a time 🔥
- 1+1 protection: One specific subset of a path for an emulated service, consisting of a standby PW and/or AC, protects another specific subset of a path for the emulated service. Traffic is permanently duplicated at the ingress node on both the currently active and standby subsets of the paths 💀
This document uses the term 'PE' to mean both PEs as per RFC 3985 [RFC3985] and T-PEs as per RFC 5659 [RFC5659] 👑
This document uses the term 'PW' to mean both PWs as per RFC 3985 and SS-PWs, MS-PWs, and PW segments as per RFC 5659 💖
2.1. Requirements Language 🌸
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119] 🎀
3. Reference Models 🧚
The following sections show the reference architecture of the PE for PW redundancy, and how that architecture gets used in different topologies and applications 💜
3.1. PE Architecture ✨
okay so Figure 1 is the PE setup for PW redundancy when more than one PW in a redundant set hangs off a single AC 💅 it's based on the architecture in Figure 4b of RFC 3985 [RFC3985] 🎀 the forwarder is the one picking which redundant PW to use, based on the criteria in this document 🧚
+----------------------------------------+
| PE Device |
+----------------------------------------+
Single | | Single | PW Instance
AC | + PW Instance X<===========>
| | |
| |----------------------|
<------>o | Single | PW Instance
| Forwarder + PW Instance X<===========>
| | |
| |----------------------|
| | Single | PW Instance
| + PW Instance X<===========>
| | |
+----------------------------------------+Figure 1: PE Architecture for PW Redundancy
3.2. PW Redundancy Network Reference Scenarios 🦋
this section gives you a set of reference scenarios for PW redundancy 🌸 they're example network topologies that show how PW redundancy gets used. you can mix them together to build bigger, more complex setups, whatever a particular app or deployment needs 💜
3.2.1. PW Redundancy for AC and PE Protection: One Dual-Homed CE with Redundant SS-PWs 💖
Figure 2 shows single-segment pseudowire redundancy where one of the CEs is dual-homed 🫶 the goal is to protect the emulated service if one of the PEs or ACs attached to that multi-homed CE fails 😭 failures in the PSN tunnels are handled by PSN mechanisms like MPLS fast reroute, so they don't end up hitting the PW 🔥
CE1 is dual-homed to PE1 and PE3 💅 a dual-homing control protocol (not covered in this doc, bestie) lets the PEs and CEs agree on which PE (PE1 or PE3) forwards toward CE1, and therefore which AC CE1 uses to forward toward the PSN ✨
|<-------------- Emulated Service ---------------->|
| |
| |<------- Pseudo Wire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC +----+ +----+ AC V
+-----+ | | PE1|==================| | | +-----+
| |----------|....|...PW1.(active)...|....|----------| |
| | | |==================| | | CE2 |
| CE1 | +----+ |PE2 | | |
| | +----+ | | +-----+
| | | |==================| |
| |----------|....|...PW2.(standby)..| |
+-----+ | | PE3|==================| |
AC +----+ +----+Figure 2: One Dual-Homed CE and Redundant SS-PWs
in this setup, only one of the PWs should be used for forwarding between PE1/PE3 and PE2 🌈 PW redundancy picks which PW goes active based on the forwarding state of the ACs, so there's only one path from CE1 to CE2 👑 that needs an extra PW state that tracks this forwarding state, separate from the PW's operational status. this is the 'Preferential Forwarding Status' 🎀
picture this: the AC from CE1 to PE1 starts out active, and the AC from CE1 to PE3 starts out standby 🍓 PW1 goes active and PW2 goes standby so the path to CE2 is complete 🦋
if the AC between CE1 and PE1 fails, the forwarding state of the AC on PE3 flips to active 😱 so PW2's preferential forwarding state needs to become active, and PW1's standby, to get connectivity between CE1 and CE2 back 💅 PE3 uses PW2 to forward toward CE2, and PE2 switches to PW2 instead of PW1 to forward toward CE1 ✨ in this scenario, the forwarding status of the ACs at PE1 and PE3 has to be signaled to PE2 so PE2 can pick which PW goes active 🫶
changes on the dual-homed side (from an AC or PE failure) don't get passed along to the ACs on the other side of the network 🙈 and failures in the PSN don't get propagated to the attached CEs either 💀
3.2.2. PW Redundancy for AC and PE Protection: Two Dual-Homed CEs with Redundant SS-PWs 🌸
Figure 3 shows single-segment pseudowire redundancy where both CEs are dual-homed 👑 this one is also built to protect the emulated service against AC and PE failures 🔥 CE1 is dual-homed to its PEs, PE1 and PE2, and CE2 is dual-homed to PE3 and PE4 💖 a dual-homing control protocol (out of scope for this doc, iykyk) lets the PEs and CEs figure out which PEs should forward toward the CEs, and therefore which ACs the CEs should use to forward toward the PSN 🧚
the PSN tunnels aren't drawn in this figure, for clarity 🎀 but you can assume each PW shown is wrapped in its own separate PSN tunnel 🦋 and just like before, protection against PSN tunnel failures comes from PSN mechanisms like MPLS fast reroute, so those failures don't affect the PW ✨
|<-------------- Emulated Service ---------------->|
| |
| |<------- Pseudowire ------->| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC +----+ +----+ AC V
+-----+ | |....|.......PW1........|....| | +-----+
| |----------| PE1|...... .........| PE3|----------| |
| CE1 | +----+ \ / PW3 +----+ | CE2 |
| | +----+ X +----+ | |
| | | |....../ \..PW4....| | | |
| |----------| PE2| | PE4|--------- | |
+-----+ | |....|.....PW2..........|....| | +-----+
AC +----+ +----+ ACFigure 3: Two Dual-Homed CEs and Redundant SS-PWs
PW1 and PW4 connect PE1 to PE3 and PE4, respectively 💅 PW2 and PW3 connect PE2 to PE4 and PE3, in the same way 💜 all four (PW1, PW2, PW3, and PW4) are up ⭐ to protect the emulated service, only one PW MUST be selected to forward traffic 🚨
if a PW's preferential forwarding status is 'active', it can carry traffic 🫧 the PEs attached to the CEs look at the combined picture and pick the one up PW to use, based on each PW's preferential forwarding status at each PE 🧚 how that status gets communicated is outside this doc's scope, so yeah, just one PW forwards ✨
here's a failure scenario that shows how PW redundancy works in Figure 3 🦋 in the starting steady state, with no AC failures, one PW is picked as active and all the others are standby 🌈 the dual-homing protocol between CE1 and PE1/PE2 picks the AC to PE2, and the one between CE2 and PE3/PE4 picks the AC to PE4 👑 so the PW between PE2 and PE4 becomes the active one to complete the path between CE1 and CE2 🍓
when the AC between dual-homed CE1 and PE2 fails, the preferential forwarding status of the PWs at PE1, PE2, PE3 and PE4 has to change so a path from CE1 to CE2 comes back 😭 different mechanisms can do that, but they're beyond this doc's scope 🙈 after the change, the algorithm has to evaluate things and select which PW forwards traffic 💅 in this app, each dual-homing algorithm, i.e., {CE1, PE1, PE2} and {CE2, PE3, PE4}, picks its active AC independently 🫶
so there's a real need to signal the active status of each AC, so the PEs can agree on a common active PW for forwarding between CE1 and CE2 🔥
changes on one side of the network from an AC or PE failure don't get propagated to the ACs on the other side 🙈 failures in the PSN don't get propagated to the attached CEs either 🫶 and heads up, end-to-end native service protection switching can also protect the emulated service in this scenario ✨ if you do that, PW3 and PW4 aren't necessary 💖
if the CEs don't do native service protection switching, they may instead load balance across the paths between the CEs 🌸
3.2.3. PW Redundancy for S-PE Protection: Single-Homed CEs with Redundant MS-PWs ✨
okay so Figure 4 🦋 shows a scenario where both CEs are single-homed 💅, and MS-PW redundancy is in use. The main goal here is to protect the emulated service when an S-PE fails 😭🫶
Native |<----------- Pseudowires ----------->| Native
Service | | Service
(AC) | |<-PSN1-->| |<-PSN2-->| | (AC)
| V V V V V V |
| +-----+ +-----+ +-----+ |
+----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+
| |-------|......PW1-Seg1.......|.PW1-Seg2......|-------| |
| CE1| | |=========| |=========| | | CE2|
| | +-----+ +-----+ +-----+ | |
+----+ |.||.| |.||.| +----+
|.||.| +-----+ |.||.|
|.||.|=========| |========== .||.|
|.||...PW2-Seg1......|.PW2-Seg2...||.|
|.| ===========|S-PE2|============ |.|
|.| +-----+ |.|
|.|============+-----+============= .|
|.....PW3-Seg1.| | PW3-Seg2......|
==============|S-PE3|===============
| |
+-----+
Figure 4: Single-Homed CE with Redundant MS-PWsCE1 is hooked up to T-PE1, and CE2 is hooked up to T-PE2 🎀 There are three multi-segment PWs: PW1 is switched at S-PE1, PW2 is switched at S-PE2, and PW3 is switched at S-PE3 🌸 This setup gives you N:1 protection for the part of the emulated service's path from T-PE1 to T-PE2 🧚
Since there's no multi-homing running on the ACs 🙈, the T-PE nodes advertise 'active' for the preferential forwarding status, based on a priority for the PW. The priority is what makes one PW the 'primary PW' and another the 'secondary PW' 👑 These priorities MUST be used if revertive mode is used, and the active PW for forwarding gets picked accordingly 💖 The priority can come from configuration, or be based on the value of the PW forwarding equivalence class (FEC). For example, a lower PWid FEC value can be taken as a higher priority ✨ But ngl, this does not guarantee that both T-PEs select the same PW, because of things like a mismatch in the PW priority configuration at each T-PE 💀 The vibe of this application is for T-PE1 and T-PE2 to sync the transmit and receive paths of the PW over the network 🫶 In other words, both T-PE nodes are required to transmit over the PW segment that is switched by the same S-PE. This is desirable for ease of operation and troubleshooting, so it's a whole mood 🌈
3.2.4. PW Redundancy for PE-rs Protection in H-VPLS Using SS-PWs 🍓
The next figure (based on the architecture shown in Figure 3 of [RFC4762]) shows how PW redundancy works in hierarchical VPLS (H-VPLS) 🦋 Heads up: the PSN tunnels aren't drawn for clarity, and only one PW of a PW group is shown. A multi-tenant unit switch (MTU-s) is dual-homed to two PE router switches 💅 This example uses SS-PWs, and the goal is to protect the emulated service against failures of a PE-rs 🎀
PE1-rs
+--------+
| VSI |
Active PW | -- |
Group..........|../ \..|.
CE-1 . | \ / | .
\ . | -- | .
\ . +--------+ .
\ MTU-s . . . PE3-rs
+--------+ . . . +--------+
| VSI | . . H-VPlS .| VSI |
| -- ..|.. . Core |.. -- |
| / \ | . PWs | / \ |
| \ /..|.. . | \ / |
| -- | . . .|.. -- |
+--------+ . . . +--------+
/ . . .
/ . +--------+ .
/ . | VSI | .
CE-2 . | -- | .
..........|../ \..|.
Standby PW | \ / |
Group | -- |
+--------+
PE2-rs
Figure 5: MTU-s Dual-Homing in H-VPLS CoreIn Figure 5, the MTU-s is dual-homed to PE1-rs and PE2-rs, and it has spoke PWs to each of them 🌷 The MTU-s needs to choose only one of the spoke PWs (the active PW) to forward traffic to one of the PEs, and it sets the other PW to standby 🧁 The MTU-s can derive the status of the PWs based on local policy configuration 🙌 PE1-rs and PE2-rs are connected to the H-VPLS core on the other side of the network 🌈 The MTU-s communicates the status of its member PWs for a set of virtual switching instances (VSIs) that share a common status of active or standby 💜 Here, the MTU-s is the one controlling which PWs get used to forward traffic 👑 Signaling with PW grouping, using a common group-id in the PWid FEC Element or a Grouping TLV in the Generalized PWid FEC Element as defined in [RFC4447], toward PE1-rs and PE2-rs, is recommended for improved scaling 📈✨
Whenever an MTU-s does a switchover of the active PW group, it needs to tell PE2-rs about this status change 💌 In other words, it lets PE2-rs know that the standby PW group has become active 🦋
In this scenario, PE devices are aware of switchovers at the MTU-s and could generate Media Access Control (MAC) Address Withdraw messages to trigger MAC flushing within the H-VPLS full mesh 🫧 By default, though, MTU-s devices should still trigger MAC Address Withdraw messages as defined in [RFC4762], so that two copies of MAC Address Withdraw messages don't get sent (one by the MTU-s and another by the PE-rs) 🙈 Mechanisms to disable the MAC withdraw trigger in certain devices are out of the scope of this document 🚫
3.2.5. PW Redundancy for PE Protection in a VPLS Ring Using SS-PWs 💍
The next figure shows how PW redundancy is used for dual-homed connectivity between PEs in a VPLS ring topology 🌸 Same as before, the PSN tunnels aren't shown, and only one PW of a PW group is drawn for clarity 🦋 This example uses SS-PWs, and the goal is to protect the emulated service against failures of a PE on the ring 💅
PE1 PE2
+--------+ +--------+
| VSI | | VSI |
| -- | | -- |
......|../ \..|.....................|../ \..|.......
| \ / | PW Group 1 | \ / |
| -- | | -- |
+--------+ +--------+
. .
. .
VPLS Domain A . . VPLS Domain B
. .
. .
. .
+--------+ +--------+
| VSI | | VSI |
| -- | | -- |
......|../ \..|.....................|../ \..|........
| \ / | PW Group 2 | \ / |
| -- | | -- |
+--------+ +--------+
PE3 PE4
Figure 6: Redundancy in a VPLS Ring TopologyIn Figure 6, PE1 and PE3 from VPLS domain A are connected to PE2 and PE4 in VPLS domain B through PW group 1 and PW group 2 🎀 The PEs are wired together so they form a ring topology 💫 Scenarios like this can come up in inter-domain H-VPLS deployments, where the Rapid Spanning Tree Protocol (RSTP) or other mechanisms may be used to keep the PW groups loop-free 🔁
[RFC4762] lays out multi-domain VPLS services, but it doesn't say how several redundant border PEs per domain and per VPLS instance can be supported 🧐 In the example above, RSTP may block PW group 1 at PE1, and it's desirable to block the group at PE2 too, by exchanging the PW preferential forwarding status of standby 🙌 How PW grouping is achieved and used is deployment specific and is outside the scope of this document 🌈
3.2.6. PW Redundancy for VPLS n-PE Protection Using SS-PWs 🪄
|<----- Provider ----->|
Core
+------+ +------+
| n-PE |::::::::::::::::::::::| n-PE |
Provider | (P) |.......... .........| (P) | Provider
Access +------+ . . +------+ Access
Network X Network
(1) +------+ . . +------+ (2)
| n-PE |.......... .........| n-PE |
| (B) |......................| (B) |
+------+ +------+
Figure 7: Bridge Module ModelFigure 7 shows a scenario with two provider access networks 🌍 This example uses SS-PWs, and the goal is to protect the emulated service against failures of a network-facing PE (n-PE) 🛡️
Each network has two n-Pes 👯 These n-PEs are connected through a full mesh of PWs for a given VPLS instance. As the figure shows, only one n-PE in each access network serves as the primary PE (P) for that VPLS instance, and the other n-PE serves as the backup PE (B) 🥹 In this figure, each primary PE has two active PWs coming out of it 😬 So when a multicast, broadcast, or unknown unicast frame arrives at the primary n-PE from the access network side, the n-PE replicates the frame over both PWs in the core, even though it only needs to send the frame over a single PW (shown with :::: in the figure) to the primary n-PE on the other side 🙃 That's unnecessary replication of customer frames, and it eats up core-network bandwidth (half of the frames get discarded at the receiving n-PE) 🗑️ It gets even worse when there are three or more n-PEs per provider access network. For example, with three n-PEs or four n-PEs per access network, 67% or 75% of the core bandwidth for multicast, broadcast, and unknown unicast is wasted, respectively 💀
In this scenario, the n-PEs can share the active or standby status of their PWs among themselves 🫶 This status can be derived from the active or backup state of an n-PE for a given VPLS ✨
4. Generic PW Redundancy Requirements 👑
4.1. Protection Switching Requirements 🌸
- okay so, 1:1 protection MUST be supported 💖 The N:1 case is less efficient with the resources you have to set aside, so it SHOULD be supported too ✨ And 1+1 protection MAY be used in the scenarios described in this doc. The details of how it's used are outside the scope of this doc, though, because it MAY require a 1+1 protection switching protocol between the CEs 🎀
- Non-revertive behavior MUST be supported 🦋 Revertive behavior is OPTIONAL. This is what keeps you from having to pick one PW as the primary unless revertive behavior is actually required 👑
- Protection switchover can be started from a PE, like with a manual switchover or a forced switchover. Or it may be triggered by a signal failure, which is a defect in the PW or PSN 💅 A manual switchover may be necessary if you need to disable one PW in a redundant set 🙈 Both methods MUST be supported, and signal failure triggers MUST be treated with a lower priority than any local or far-end forced switch or manual trigger. Priority check, bestie 🔥
- A PE MAY be able to forward packets it gets from a PW with a standby status, so in-flight packets don't get black-holed during switchover 🧚 But if VPLS is in use, all VPLS application packets received from standby PWs MUST be dropped, except for OAM and control-plane packets. No cap, this one is important 😭
4.2. Operational Requirements 🧚
- (T-)PEs involved in protecting a PW SHOULD automatically discover and try to resolve inconsistencies in the configuration of primary/secondary PWs 🌈
- (T-)PEs involved in protecting a PW SHOULD automatically discover and try to resolve inconsistencies in the configuration of revertive/non-revertive protection switching mode 💜
- (T-)PEs that don't automatically discover or resolve inconsistencies in the configuration of primary/secondary, revertive/non-revertive, or other parameters MUST generate an alarm when they detect an inconsistent configuration 🚨
- (T-)PEs participating in PW redundancy MUST support the configuration of revertive or non-revertive protection switching modes, if both modes are supported 🎀
- The MIB(s) MUST support inter-PSN monitoring of the PW redundancy configuration, including the protection switching mode 🍓
- (T-)PEs participating in PW redundancy SHOULD support the local invocation of protection switching ⭐
- (T-)PEs participating in PW redundancy SHOULD support the local invocation of a lockout of protection switching ✨
5. Security Considerations 💅
The PW redundancy method described in this RFC will require an extension to the PW setup and maintenance protocol [RFC4447], which in turn is carried over the Label Distribution Protocol (LDP) [RFC5036]. So this PW redundancy method will inherit the security mechanisms of whatever version of LDP is implemented in the PEs. Take that seriously, bestie, because your security is only as strong as the LDP underneath it 😭🔒
6. Contributors 🫶
The editors would like to thank Pranjal Kumar Dutta, Marc Lasserre, Jonathan Newton, Hamid Ould-Brahim, Olen Stokes, Dave Mcdysan, Giles Heron, and Thomas Nadeau, all of whom made a major contribution to the development of this document 💖
Pranjal Dutta — Alcatel-Lucent — EMail: pranjal.dutta@alcatel-lucent.com
Marc Lasserre — Alcatel-Lucent — EMail: marc.lasserre@alcatel-lucent.com
Jonathan Newton — Cable & Wireless — EMail: Jonathan.Newton@cw.com
Hamid Ould-Brahim — EMail: ouldh@yahoo.com
Olen Stokes — Extreme Networks — EMail: ostokes@extremenetworks.com
Dave McDysan — Verizon — EMail: dave.mcdysan@verizon.com
Giles Heron — Cisco Systems — EMail: giles.heron@gmail.com
Thomas Nadeau — Juniper Networks — EMail: tnadeau@lucidvision.com
7. Acknowledgements 💜
The authors would like to thank Vach Kompella, Kendall Harvey, Tiberiu Grigoriu, Neil Hart, Kajal Saha, Florin Balus, and Philippe Niger for their valuable comments and suggestions 🌸
8. References 🦋
8.1. Normative References
- [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
- [RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.
- [RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual Private Network (VPN) Terminology", RFC 4026, March 2005.
- [RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
- [RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G. Heron, "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", RFC 4447, April 2006.
- [RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC 4762, January 2007.
- [RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP Specification", RFC 5036, October 2007.
- [RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-Segment Pseudowire Emulation Edge-to-Edge", RFC 5659, October 2009.
8.2. Informative Reference
- [RFC5601] Nadeau, T. and D. Zelig, "Pseudowire (PW) Management Information Base (MIB)", RFC 5601, July 2009.
Authors' Addresses 💖
Praveen Muley — Alcatel-Lucent — EMail: praveen.muley@alcatel-lucent.com
Mustapha Aissaoui — Alcatel-Lucent — EMail: mustapha.aissaoui@alcatel-lucent.com
Matthew Bocci — Alcatel-Lucent — EMail: matthew.bocci@alcatel-lucent.com 🧚
📦 where this page comes from
- ietf: rfc6718 2012-08
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms